Stretch film

Abstract

Stretch films are disclosed, the films having at least one layer formed of or including a polyethylene copolymer and having a natural draw ratio of at least 250%, a tensile stress at the natural draw ratio of at least 22 MPa, and a tensile stress at second yield of at least 12 MPa. In some embodiments, the polyethylene copolymer can have a CDBI of at least 70%, a melt index I 2.16 of from 0.1 to 15 g/10 min., a density of from 0.910 to 0.940 g/cm 3 , a melt index ratio I 21.6 /I 2.16 of from 30 to 80, and an Mw/Mn ratio of from 2.5 to 5.5. The stretch films are particularly useful in bundling and packaging applications.

1. A wrapped article comprising:
 an article; 
 a stretch film; 
 wherein the stretch film is elongated to the yield plateau and less than the natural draw ratio; and 
 the article is wrapped with the stretch film, the stretch film comprising: 
 at least one first layer; and 
 at least one second layer not comprising a LDPE, wherein any one or more layers comprises a polyethylene copolymer with a Compositional Distribution Breadth Index (CDBI) of at least 70%, a melt index I 2.16  of from 0.1 to 15 g/10 min., a density of from 0.910 to 0.940 g/cm 3 , a melt index ratio I 21.6 /I 2.16  of from 30 to 80, and an Mw/Mn ratio of from 2.5 to 5.5 and from 0.25 to 6 wt % of one or more tackifiers, wherein: 
 the film having a natural draw ratio of at least 250%, a tensile stress at the natural draw ratio of at least 22 MPa, and a tensile stress at second yield point of at least 12 MPa, as measured according to ASTM D-882/97; and 
 the film having a yield plateau having a linear portion with a slope of at least 0.020 MPa per % elongation interposed between the second yield point and the natural draw ratio. 
 
     
     
       2. The wrapped article of  claim 1 , wherein the film has a dart impact strength D, a modulus M, where M is the arithmetic mean of the machine direction and transverse direction 1% secant moduli, and a relation between D in g/μm and M in MPa such that: 
       
         
           
             
               D 
               ≥ 
               
                 
                   0.0315 
                   [ 
                   
                     100 
                     + 
                     
                       ⅇ 
                       
                         ( 
                         
                           11.71 
                           - 
                           
                             0.03887 
                             ⁢ 
                             M 
                           
                           + 
                           
                             4.592 
                             × 
                             
                               10 
                               
                                 - 
                                 5 
                               
                             
                             ⁢ 
                             
                               M 
                               2 
                             
                           
                         
                         ) 
                       
                     
                   
                   ] 
                 
                 . 
               
             
           
         
       
     
     
       3. The wrapped article of  claim 1 , wherein the tensile stress at the natural draw ratio is at least 26 MPa, and the natural draw ratio is at least 300%. 
     
     
       4. The wrapped article of  claim 1 , wherein the film has a tensile stress at first yield of at least 9 MPa, and a second yield of at least 14 MPa, both yields measured according to ASTM D-882/97. 
     
     
       5. The wrapped article of  claim 1 , wherein the CDBI is at least 85%; the melt index ratio is from 35 to 60; and the Mw/Mn ratio is from 3.0 to 4.0. 
     
     
       6. The wrapped article of  claim 1 , wherein the melt index is from 0.3 to 10 g/10 min, and the density is from 0.918 to 0.935 g/cm 3 . 
     
     
       7. The wrapped article of  claim 1 , wherein the stretch film is provided in a pre-stretched condition.